The subject matter of the invention concerns compositions for the oxidative dyeing of hair based on 4,5-diaminopyrazole derivatives as developers and new 4,5-diaminopyrazole derivatives.
In the area of hair coloring, oxidative dyes have achieved considerable importance. The dyeing is effected by the reaction of certain developers with certain couplers in the presence of a suitable oxidizing agent.
Such developers are, in particular, 2,5-diaminotoluene, 2,5-diaminophenylethyl alcohol, p-aminophenol and 1,4-diaminobenzene. Resorcinol, 4-chlororesorcinol, 1-naphthol, 3-aminophenol, 5-amino-2-methylphenol and derivatives of m-phenylenediamine are preferably used as couplers.
Oxidative dye compositions for dyeing human hair have numerous special requirements. For example, they must be unobjectionable in toxicological and dermatological respects and must enable the desired intensity of coloring. In addition, a favorable fastness to light, permanent waving, acids and rubbing is required of the achieved hair dyes. But, in every instance, such hair dyes must remain stable over a period of at least 4 to 6 weeks without being affected by light, rubbing or chemical agents. Moreover, it is necessary that a wide assortment of various color shades can be produced by means of combining suitable developers and couplers. 4-Aminophenol above all is used to achieve natural shades and especially fashionable shades in the red range either by itself or in a mixture with other developers in combination with suitable couplers.
The developer 4-aminophenol, whose chief use was formerly for the red range of the color scale, has been criticized in the past with respect to its physiological compatibility, while developers such as pyrimidine derivatives which have been recommended more recently are not completely satisfactory with respect to coloring. The pyrazole derivatives described in DE-OS21 60 317 such as 3-amino-1-phenyl-2-pyrazolone-5 have insufficient depth of color when used to dye hair and are not usable in hair dyeing practice.
Pyrazole derivatives which achieve intense coloring with various couplers are described in DE-OS 38 43 892. The compounds described therein can only be obtained by very expensive synthesizing processes and have low yields.
Various methods have been described in technical literature for producing 1-methyl-4,5-diaminopyrazole. According to H. Dorn, et al., Chem. Ber. 98, p. 3368 (1965), 5-amino-1-methylpyrazole-4-carboxylic acid is obtained in a yield of 53 percent from ethoxymethylene cyanoacetic acid ethyl ester and methylhydrazine and is decarboxylated to obtain 5-amino-1-methylpyrazole with a yield of 75 percent (total yield : 40 percent). DE-OS 2 141 700 describes a single-step process for obtaining 5-amino-1-methylpyrazole from N,N-dimethylaminoacrylonitrile and methylhydrazine in a yield of 71 percent. For further conversion, this compound can be convened to 5-amino-1-methyl-4-nitropyrazole with a yield of 23 percent according to M. A. Khan, et al., Can. J. Chem. 49, p. 3566 (1971).
According to V. P. Perevalov, et al., Khim. Geterotsicl. Soedin. 8, p. 1090 (1985), catalytic reduction of this product produces 1-methyl-4,5-diaminopyrazole dihydrochloride with a yield of approximately 79 percent. According to this reaction sequence, the total yield of 1-methyl-4,5-diaminopyrazole amounts to 13 percent throughout all steps.
Better yields are obtained when 5-amino-1-methylpyrazole is converted with isoamyl nitrite, according to H. Dorn, et al., Liebigs Ann. Chem. 717, p. 118 (1968), to produce 5-amino-1-methyl-4-nitrosopyrazole (gross yield approximately 97 percent) and then reduced with tin(II)chloride to give the end product (yield: 67 percent) so that the total yield according to this process is 46 percent throughout all steps.
A corresponding synthesis for 1-benzyl-4,5-diaminopyrazole is described in DE-OS 34 32 983. 5-Amino-1-benzylpyrazole-4-carboxylic acid ethyl ester is obtained from ethoxymethylene cyanoacetic acid ethyl ester and benzylhydrazine. After cleavage of the ester, decarboxylation, nitrozation and reduction, 1-benzyl-4,5-diaminopyrazole is obtained in a total yield of 30 percent.
Aside from low yields in some cases, the described processes exhibit other disadvantages. For example, it has not been taken into account that starting compounds such as ethoxymethyl cyanoacetic acid ethyl ester and N,N-dimethylaminoacrylonitrile as well as certain hydrazine derivatives are not available commercially and in some cases must be produced by costly syntheses. Moreover, commercially available hydrazine derivatives are classified as poisonous and in some cases as suspected carcinogens. Further, the production of compounds substituted in the 5-position amino group (e.g., alkyl, hydroxyalkyl, benzyl) is not described in this process or by subsequent steps. A further disadvantage of this synthesis consists in that the ring alkylation is already introduced in the first reaction step, that is, special starting compounds are already required at the start of the synthesis.
Under these conditions, alkylation on the ring nitrogen of a pyrazole derivative substituted in the 4-position or 5-position would be more advisable so that different derivatives are achieved only at the end of the synthesis through the selection of different alkylating agents. A process for the production of 1-methyl-4,5-diaminopyrazole is described in DE-OS 38 43 892. According to this process, 3(5)-amino-4-nitropyrazole--which is formed in a total yield of approximately 41 percent by cyclization of 2-chloroacrylonitrile with hydrazine (G. Ege, Angew. Chem., 86, p. 237 (1974)) and subsequent acetylation of the amino group, nitration and separation of the protective group--is alkylated with dimethyl sulfate to give an isomeric mixture in a yield of 70 percent which can be separated by chromatography to give the desired 5-amino-1-methyl-4-nitropyrazole in a yield of 25 percent and the isomeric 3-amino-1-methyl-4-nitropyrazole in a yield of 45 percent. The corresponding diamino compounds were isolated after reduction of the nitro compounds.
DE-OS 38 43 892 describes conversion of 3(5)-amino-4-nitropyrazole with benzyl bromide. The desired 5-amino-1-benzyl-4-nitropyrazole is not formed. Rather, a mixture is obtained from which approximately 18 percent 1-benzyl-3-benzylamino-4-nitropyrazole and 78 percent 3-amino-1-benzyl-4-nitropyrazole are obtained after chromatographic separation.
This process also provides very poor yield, if any, of substituted pyrazole derivatives such as 5-amino-1-alkyl-4-nitropyrazole or 5-amino-1-benzyl-4-nitropyrazole and compounds substituted in the 5-amino group which can be converted to the corresponding diamino compounds by reduction. Further, this process also requires the use of hydrazine which has been criticized.